1. Field of the Invention
The present invention relates to a bulldozer blade pitch control method and a controller for the same, for automatically resetting a bulldozer blade to a predetermined excavating pitch while the bulldozer is traveling backwardly after the bulldozer has completed an operation of excavating, carrying, or dumping earth.
2. Description of Related Art
As shown in FIG. 3, a bulldozer 20, which is equipped with a bulldozer blade 10, has a left frame member 15A and a right frame member 15B which are pivotally attached to the right and left sides of the vehicle body 20a of the bulldozer 20 such that they can swing, the bulldozer blade 10 being pivotally installed on the leading ends of the frame members 15A and 15B so that the bulldozer blade 10 can swing longitudinally. The left end portion of the bulldozer blade 10 is pivotally connected to one end of the left pitching cylinder 20A, while the other end of the left pitching cylinder 20A is connected to an intermediate portion of the left frame member 15A. Similarly, the right end portion of the bulldozer blade 10 is pivotally connected to one end of the right pitching cylinder 20B, while the other end of the right pitching cylinder 20B is connected to an intermediate portion of the right frame member 15B.
The left portion of the bulldozer blade 10 is also pivotally connected to the left front portion of the vehicle body 20a by the left lifting cylinder 21A, while the right portion of the bulldozer blade 10 is also pivotally connected to the right front portion of the vehicle body 20b by the right lifting cylinder 21B. The lifting cylinders 21A and 21B can be extended or retracted simultaneously so as to raise or lower the bulldozer blade 10 as indicated by the arrow A in FIG. 3. The pitching cylinders 20A and 20B can be extended or retracted simultaneously to pitch the bulldozer blade 10 forwardly for dumping or backwardly as indicated by the arrow B in FIG. 3.
In a conventional bulldozer, for example, as proposed in Japanese Unexamined Utility Model Publication No. 3-50646, the bulldozer blade is raised, lowered, and pitched by a single control lever and a single tilting or pitching selector switch.
When the bulldozer excavates while traveling forwardly, the bulldozer blade is pitched at an excavation angle. When the bulldozer carries earth while traveling forwardly, the bulldozer blade is pitched backwardly from the excavating angle to a carrying pitch, also known as a back pitch. The term "earth" is considered to be generic to dirt, sand, rocks, debris, etc., which can be excavated and carried by a bulldozer. When the bulldozer dumps earth while traveling forwardly, the bulldozer blade is forwardly from the excavating angle to a dumping pitch. However, when an operator of the bulldozer returns to an original excavating point by traveling the bulldozer backwardly after completing such carrying or dumping work, the operator is required to simultaneously operate both the control lever for steering the bulldozer and a working machine lever for resetting the bulldozer blade to the original excavating pitch. This makes the operation complicated, which is undesirable from a safety standpoint.